Method of and means for controlling the operation of heat exchange devices



' June 29, 1937. .P. BORCHARDT ET AL METHOD OF AND MEANS FOR CONTROLLING THE OPERATION OF HEAT EXCHANGE DEVICES 2 Sheets-Sheet 1 M Mr N 1% H SF aw IITII'I r dn v v TIME MIN.

HANS PARKE ATTORNEY AIR Jun 9, 1.937. P. BORCHARDT ET AL METHOD OF AND MEANS FOR CONTROLLING THE OPERATION OF HEAT EXCHANGE DEVICES 2 Sheets-Sheet? INVENTORS PHIL/PP BORCHARDT Filed Jan. 9, 1934' f/ANS RAN/(E BY ATTORNEY Patented June 29, 1937 LING THE OPERATION CHANGE DEVICES OF HEAT EX- Philipp Borchardt anrLHans Ranke, Solln, near Munich, Germany, assignors, by mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York Application January 9, 1934, Serial No. 705,976 In Germany January 17, 19 33 17 Claims. (01. 62-1755) The present invention relates to control methods and systems, and-particularly to such-methods and systems in which the volume of a gaseous fluid flowing through, or discharged by, a plurality of receptacles or heat exchange devices is controlled by the temperature of the gaseous fluid.

In the separation of gas mixtures into their components by liquefaction it is customary to use heat exchange devices or regenerators in order to make the heat exchange between the incoming fresh gas and the products of the separation as perfect as possible. A satisfactory heat exchange, however, is possible only if the heat content which the fresh gas gives up to the regenerator in the state of equilibrium is exactly @qual to that which is requiredby the separation product to heat it'to the temperature at which the fresh gas enters the heat exchange device, that is, if the difierence in heat content for both gases at both ends of the device is exactly the same. Furthermore, in gas separation plants a number of such devices or regenerators are necessary; in the separation of air, for example, two are needed for oxygen and two for nitrogen. The problem, therefore, is to distribute the fresh gas and the separation products among the individual regenerators in such' a way that the above condition is complied with for each individual regenerator.

If the heat exchange is accomplished in socalled counter-current coolers, such a distribution of the gas quantities is likewise necessary; however, in this case no difilculties are presented because the heat capacity of the counter-current cooler is so low in relation to the heat capacity of the gases flowing therethrough, that when the volumes of gas flowing therethrough are varied, the new permanent state of equilibrium is attained in a short period of time. suflicient to control the discharge temperature of the separation products coming out of the heat exchange device, whereby each error in distribution becomes immediately noticeable through the "decrease of the discharge temperature of one gas in comparison to that of the other. No difiicul ties are thus presented in carrying out the distribution in such a manner that the difference in heat content of the outgoing separation prod generators, if a change is made in the volume of time,- often not for several hours.

It is thereforemethod used for counter-current coolers is therefore impracticable, and it appears to be impossible, for example, to correctly distribute the incoming gas to four regenerators operating in parallel, and to simultaneously benefit, in a practical manner, from the advantages which are theoretically ofl'ered by the use of regenerators.

The present invention makes it possible to overcome this dimculty and to correct-unbalances or errors in distribution automatically and immediately, regardless of the length ofthe adjusting period of the regenerators taken as a whole.

The invention is based upon the observation that even when utilizing exceedingly large storing devices or regenerators, the temperatures at the cold end of a regenerator vary in a relatively close manner with the changes in the gas volumes flowing therethrough. These temperatures, and especially the temperature difference between the incoming gas and the products of the separation,

do not remain constant during any one period of flow in one direction, but rather change continuously, particularly towards the end of a period; their course during a double period to a certain degree resembles a hysteresis-loop. The temperature difference between fresh gas and separation product at the end of a warming period, however, is largely dependent upon whether the separation product in the previous period yielded too much or too little cold content to the regenerators. This invention contemplates taking advantage of the diiference in temperature existing between the gas mixture which is to be separated on the one hand, and the separated gases on the other hand, as measured at the cold end of the regenerators, toward the end of a period of flow in one direction, for the purpose of automatically controlling the volumes of gas passing through the r egenerator. This may be accomplished, for example, by means of temperature responsive devices, such as thermometers which are located in the gas ducts, and other suitable control devices.

One particular embodiment of this invention will now be described in connection with the accompanying drawings in which:

Fig. 1 represents a schematic diagram showing the temperature variations at the cold end of a Referring more particularly to Fig. 1 the curves shown represent thetemperature variations at the cold end of a regenerator in operation as a heat exchange device'between oxygen and air, as

a function of time during a period of gas flow in one direction. The ordinate indicates the temperature in degrees centigrade absolute, and the abscissa the time in minutes. The oxygen flowing into the regenerator during a period of flow in. one direction has a substantially constant temperature which is approximately its temperature of evaporation. Following the reversal of gas flow, the compressed air which flows through the regenerator in the opposite direction initially is cooled to the same temperature as'the oxygen, except for the slight difference caused by the losses incurred during the heat transfer from the gas to the gratings of the regenerator and thence back again to the gas. However, towards the end of. the period of flow in one direction the temperature of the air rises steadily because the a temperature of the regenerator increases. It the air volume is correctly regulated with respect to .the separated gas, the temperature of the air will, for example, follow the course shown in the diagram by the solid line. The rise in temperature towards the end of the period of flow in one direction is caused by the unavoidable difference in heat content between the compressed air and the expanded separated gas. If too much air flows through the regenerator in relation to the volume of the separated gas, then the temperature of the air will rise much higher in the second half of the period, especially towards the end, as shown in the upper broken line. If the air volume is too small, then the temperature of the air towards the end of the reversal period will remain close to that of the separation product. If, towards the end of a reversal period, a'regenerator supplies to the separation plant, air which is too hot, then the impurities in the air, such as carbon dioxide and nitrous oxide,-which are desired to be re versibly retained in the regenerators, will only be partially separated and will consequently reach cumulate and thus cause serious difliculties.

Referring now more particularly to Fig. 2 of the drawings, a two-stage air rectifying apparatus is shown at 5. The nitrogen discharged at 6 yields in heat exchange relation with the major portion of the 'air, while the oxygen leaving the separating apparatus at I yields its cold content, in the regenerator-pair 3, 4, to the remainder of regenerators at ll, l2, l3 and M, temperature indicating' devices, such as thermometers are located in the various ducts. Use may be made, for, example, of resistance thermometers, whose timelag is so low that they readily follow the fluctuations of the temperatures during each period of reversal. The resistance thermometers II and I2 are connected to constitute two branches of a Wheatstone bridge circuit, the thermometers i3 and 14 forming the corresponding banches of a second bridge circuit. A so-called drop-bail instrument I6 is utilized as zero instrument in the bridges, which is so adjusted that the bails are depressed at the end of each regenerator period and approximately 10 to 20 seconds before the rethe separation apparatus, in which they will acits cold content to the pair of regenerators I, 2'

the air to be separated. At the cold .end of the aosacer I versal of the regenerators. This instrument is described in detail on pages 96, 97 and 98 of a r publication entitled Der Chemie--Ingenieur", vol. 2, part I, 1932. The bridge circuit and the sensitivity of the instrument are preferably so adjusted that the'instrument closes a circuit when the temperature difference between air-and separation products exceeds or falls below a certain temperature range. If, for example, the temperature difierence between air and separation-product amounts to 6 when the valve adjustment of the regenerators is correct, then, the bridge ap' duced when the temperature difference exceeds 8, and is increased when the temperature difference falls below 6". -The reversal of the re; generators is accomplished by the periodic operation of the reversal valves 2i, 22', 23' and 24' located in the conduits between the throttle valves 2|, 22, 23 and 24 and the respective regenerators I, 2, 3 and 4. The switching apparatus [5 also reverses the regenerators l, 2, 3 and 4 after regular periods of time, e. g. by transmitting impulses to' the reversing valves 2|, 22', 23' and t 24' at intervals of .three minutes, in such a manner that for a period'of three minutes nitrogen fiows through regenerator i and air through regenerator 2, whereas for the next three minutes air flows through regenerator I and nitrogen through regenerator 2. In the same manner, oxygen and air are alternately caused to flow through regenerators 3 and l. The switching apparatus l5 also connects the thermometers H, i2, i3, i4 through lines 2, 2i2, 2l3,'2|4 to the control instrument I6 over line 35 one-half of a minute prior to the end of the cycle during which air flows through the respective regenerator. Thus, the thermometers transmit their measuring values successively to the drop-bail instrument [6; The contact bars of the instrument [6 are depressed a few seconds prior to the endof the cycle, and thus the relays ill-34, 4I-44, 5l-54 (Fig. 3) which are located in the relay bo x ii are operated over lines 36, 31, 38 and l3l-I3l,

i4 i-IM, l5l-l 54 according to whether the tem an excess of control or over-regulation would re-.

This .difipculty may be obviated either by efiecting a control operation only at intervals of suit.

from fiveto ten reversals, or by providing a suitable feed-back or return impulse. The feed-back may preferably be accomplished by electrical means, in that simultaneously with the regulating operation, the bridge circuit is so adjusted 75 by-the insertion or shunting of additional resistances, that the change in the temperature difference in the state of equilibrium corresponding to one operation has already progressed part way, for. example, to one-third. The feed-back impulse is or may be cancelled at the subsequent measurement of the temperature difference at the same regenerator, during which the drop-bail instrument remains in the rest position.

Only a single drop-bail instrument is required for connection with all of the regenerators. If

the reversal period of a regenerator-pair, for example, amounts to three minutes, then the reversals of the two pairs are spaced one and onehalf minutes apart, so that a reversal occurs every minute and a half. By means of the time switch IS the drop-bail instrument is switched into the proper bridge circuit approximately one minute before each reversal of the regenerators, and, for example, ten seconds before the regenerator-pair is reversed, the balls or bars of the instrument are depressed, whereby that particular valve is.

actuated through which the air enters into the regenerator which is momentarily traversed by air.

One-half minute following the reversal, the dropbail instrument is switched bythe time switch into that bridge circuit which is connected to the regenerator to be reversed one and one-half minutes later.

The principle of the invention, .that is, automatically controlling the gas volumes flowing through regenerators by means of the regenerator temperatures, can be applied in other ways than shown in the above-embodiment. For example,

1 instead of the temperature difference between separation product and fresh gas, it is also possible to usea predetermined absolute temperature of the fresh gas at the cold end of the regenerator as a control. Another method of operation is that the temperature difference between two regenerators of a pair is utilized for regulating the volumes. In this case the thermometers are preferably located in the cold half of the regenerators. Mechanical thermometers, such as metal thermometers, gas thermometers, and vapor pressure thermometers may be used asgtemperature Indicating devices; however,- electrical thermometers (thermoelements or resistance thermometers) possess the advantage of direct electric transmission. The modification of the invention which has been described above is based on the assumption that the most favorable distribution of the air volumes to the various regenerators will result in a certain difference in temperature betweenthe fresh gas and the separation product at the cold end of the regenerators, a difference caused by the change in the heat contents with changes in pressure, as well as by the unavoidable losses in refrigeration. Thus, a change in the volumes of gas flowing through the individual regenerators is produced when the temperature of the cooled air deviates from an assumed average or normal figure. This method entails the difiiculty that the adjustment to this normal figure for the temperature difference is impossible without arbitrary assumptions in regard to the heat exchange conditions in the regenerators, etc., and that even when the correct normal figure for .the temperature difference has been obtained, it is liable to be affected or varied by changes in the refrigeratingconditions, etc. If, for example, the value of the assumed normal temperature difference is increased for any'reason during operation, the automatic regulation described above will reduce the air supply to all regenerators, even though the distribution of the air to the various regenerators is correct. The only change resulting from this is that of the total volume of air discharged. However, inasmuch as the volume of the separated components of the air ischanged to the same extent, there is no change in the relation of the heat contents exchanged'through the regenerators, so that this method does not compensate for any false temperatures, but rather only disturbs the operation by detrimentally affecting the production. The control system described above is too sensitive because of its adjusting of the volumes of fresh gas passing through a single regenerator without consideration of the fact that the total volume of fresh gas passing through the regenerators is predetermined or constant and by changing the volume of gas passing through one regenerator, the rate of flow through all the other regenerators is necessarily affected. In order to obviate these difficulties, it isa further feature of this invention to measure and-regulate the flow of gas through the various regenerators in a manner which takes into consideration the.

mutual dependence of the individual regenerators in the distribution of the total volume of incoming gas. According to this feature of the invention, the distribution of the freshgas volumes is accomplished in such a manner that there is first obtained a mean or average value of the individual regulating measurements, and,

that then a change is made in the air supply of only those regenerators whose temperature deviates from this mean value, so that the sum .total of the absolute temperature differences of the individual regenerators as compared to the mean value of their temperatures tends to ap-.

between the'remainder of the air and the oxygen.

The control measurements are effected with the aid of resistance thermometers a fewseconds be- We shall assumefore the end of the period of flow in one direction. The absolute temperature of the air at the cold end of the regenerators is measured and the measurements. are transmitted to a Wheatstone bridge circuit, or preferably directly to a crossedcoil-drop-bail instrument. The mode of operation of a crossed-coil instrument has been described in a publication entitledz' Der Chemic- Ingenieur vol. 2, part I, 1932, on pages 54 and 55.

The impulses produced by the drop-bail instrument in accordance with the control measurements are notdirectly utilized for regulating the throttle valves in the air supply lines to the regenerators, but their mean value is first de-. termined by means of a switching or compensating apparatus; and a control operation is initiv relays correspond to box I! of Fig. 2).v

figure also shows the valve control relays 3| to,

' only if all four regenerators have transmitted lays at to 34, 4| to 44, 5| to 54 (these twelve This 64 and II to 14 (these latter relays correspond to the box I9 of Fig. 2), and the'connecting lines. The last digits 1 to 4 of these referenc'enumbers indicate that the relay or element referred to corresponds to one of the regenerators identified by numerals I to 4 in Fig. 2. After each control measurement of one of the thermometers II, l2,

I3, or 4, the drop-bail instrument I6 may transput one of 3 possible control impulses over the relays II. to the disc I8. In other words the temperature measured will either be within the predetermined range of fluctuation within the lays 3! to 34, 4| to 44 or 5| to 54 is conditioned or prepared for operation over lines |3| to I34, MI to I44 or |5| to I54, but the switch 26, which controls the circuit including lines 55 and 58 leading to the control relays 6! to 64, II to 14 is still open and consequently the closing of these relays does not operate the valves. Simultaneously with the conditioning of relays 3| to 34, 4| to 44, or 5| to 54, the disc I8 is rotated, in the direction of the existing'unbalance, f th of its circumference, by virtue of the current impulse transmitted by the drop-bail instrument. If the temperature measurement at one of the regenerators to 4 shows that the temperature of the air is lower than the normal value, one of the relays 3i to 34 will be operated and the disc l8 will be rotated in a counterclockwise direction. If the measurement shows that the air leaving the regenerator is too hot, then one of the relays 5| to 54 is operated and the disc is turned clockwise. If the instrument measures the desired or-normal value for the air temperature, then only relays 4| 'to 44 are operated, while the switching-disc I8 remains stationary. 1

Since the temperature of the air leaving the regenerators is measured toward the end of the periods of three minutes during which air flows through the regenerators, and since the movements at which the direction of flow of the oxygen and nitrogen regenerators are reversed.

The mean value of the individual temperatures is determined by virtue of the fact that an operation of the throttle valves 2| to 24 through the closing of'the switch 26 can be eifected over relays 6| to 64, or II to T4, and lines 22| to 224 their measurement impulses to the relays 3| to 34, 4| to 44, 5| to 54 of the switching disc I8, and that after each 4 measurements, the switch disc I8 has a position which is the sum total of the four individual displacements. If, for example, two regenerators are too cold and two too hot, then the movements of the disc caused by the individual temperature measurements equalize one another. -If three regenerators are too warm and one too cold, then the disc, will be turned clockwise fortwo units out of its normal position.

The formation of the average temperature value, which is automatically derived by virtue of the arrival of individual correcting impulses, furnishes the desired mean value of, the regenerator temperatures and produces the following effect upon the control of the throttle valves: After all four regenerators have transmitted their impulses over the drop-bail instrument to the relays 3| to 34, 4| to 44 and 5| to 54, switch 26 is actuated; this switch closes, over lines 55 and 58 the circuits in'which are located the relays 6| to 64 and lines IBI to I64 for opening the throttle valves, or the relays II to 14 over lines Ill to I14 for closing the throttle valves, as the case may be. It will be appreciated that not every one of the relays 3| to 34, 4| to 44 or 5i to 54 is in a condition to effect a control operation, but only those whose contactors |0| to I04, III to |i4,'or I2I to I24 are conductively connected through metallic members 8| to 84, or

9| to 34, respectively, to the operating relays. In 7 this manner, the air supplied to those regenerators only whose temperature is different from the desired mean temperature is controlled. The

over lines :51, I53, I32 and m. The distributor disc l8 assumes the position shown in the draw-v ings, since the individual displacements have compensated each other. Thus, relays 32 and 34 are connected to relays 62 and 64 over conductors 232, 234, contact springs I02, I04 and conductors 82 and 84; also the relays 5| and 53 are connected over lines and 253, contact springs HI and I23, conductors 9| and 93 to the relays II and I3, so that after the determinationof the mean value, all the temperature measurements initiate control operations because the tempera ture of all the regenerators deviates from the mean value. Therefore, after the switch 26 is closed the air supply 'to the regenerators and 3 is reduced, by closing the throttle valves 2| and 23 a certain amount over lines MI and 223 by the operation of relays II and 13 while that to regenerators 2 and 4 is increased by opening the throttle valves 22 and 24 a certain amount by means of relays 62 and 64, which transmit their impulse to the respective valves over lines 222 and'224. The impulse delivered to the valves by relays 6| to 64 over lines 22| to 224 is of opposite sign, e. g. positive, as compared to the impulse dolivered over the same lines by relays II to 14, e. g. negative. This is necessary so that operation of relays 6| to 64 will cause an opening movement while that of relays II and I4 will cause a closing movement as described. To furnish such impulses the movable contaotors of relays 6| to 64 may be connected to the positive pole of a battery 19 of an even number of cells while the negative pole of the battery is connected to the contactors ofrelays II to 14 and the midpoint connector of the battery is grounded. The circuits are completed by grounding one connection of each valve operating motor, the other being connected to the respective lead 22| to 224 as shown.

Assume, in another case, that all four regenerample. that an error was made in selecting the normal temperature. In this event, it is true that all relays 3|to 34 are brought into switching preparation by the temperature measurements, however, the switching disc was simultaneously turned counter-clockwise by four units, that is, a total of 90, so that the conductor bars or strips 8| to 84 no longer touch contactors |8| to I84 and even after the closing of the switch 28, the circuit leading to the relays 6| to 64 remains open. Although the bars 9| to 94 are then touching contactors |2| to I24 and I to 4, the relays 5| to 54 and 4| to 44 are open so that relays H to 14 also remain open and no change of the valves 2| to 24 is made and the distribution of air among the regenerators is not changed. Thus an error in selecting the. normal temperature does not upset the distribu- 4 tion and the condition is to be corrected by se lecting a new normal or changing the total quantity of air supplied.

In general, a regulation of the air supply to the individual regenerators is eflected only in the instances given in the table below. Thecolumns of the table give the number of regenerators which find themselves in a certain state, while the letters beside'the figures characterize the special state;- n indicates that the air passing out of the regenerator is of the desired or normal temperature; It means that it is too cold, and to that it is too warm. Those regenerators to which the air supply is changed following the mean value determination are underlined,

' r Y Displacements Position of the oi the disc after Result of the regulating switching disc iour regulating measurement I measurements Unchanged EL 21121 411 Number oi'shiits toward cold.' 1 3nl l 1 111 23 2 n 1 a a 1 n a k 4' 4 k Numberoi shifts towardwarm 1 3nl w lnl k2 v n 1 15 1' 3 Ln 3 w 4 4 w After the throttle valves have been regulated through switch 26 over relays 6| to 64 or H to 14 and lines 22| to 224 in the underlined instances, the disc I 8 isireturned to the starting position and switch 26 is opened. The switch 26 is coupled in suitable fashion with the switching machine l which reverses the direction of flow of the gases through the regenerators. l

By determining the mean value prior to a control operation, the temperature measurements of all regenerators have the same weight. That is; no consideration is given to the volume of the air which flows through the individual regenerator. In view of this; the mean value of the regenerator temperatures determined for the purpose of regulation need not agree with the effectivetemperature of the air leaving the regenerators. However, this does not produce operation, inasmuch as the throttle valves operated following the mean value determination are adapted to the air volume flowing through the regenerator in question, so that when they are operated, the individual measurements are automatically interpreted according to the volume of air flowing through regenerator.

'In the event the fresh gas is to be distributed to more than four regenerators, the principle oi. the invention may be practiced in substantially the same manner. In .this event, an additional relay is inserted in each group of relays 3| to 34, 4|

to 44 and 5| to 54 and an additional accompanying conductive strip is secured adjacent to each set of strips'Bl to 84 and 9| to 94 for each additional regenerator.- The number of displacements which position the bars 8| to 84 and 8| to 94 in the zero setting of the switching apparatus in front of the contact springs I to H4 is equal to one-half the number of the individual measurements, that is, when using six regenerators, three displacements, before the zero setting, and four when using eight regenerators. I

It is furthermore possible with the described apparatus to separate the regulation ofthe fresh gas distribution to the individual regenerators into several stages. In this event, additional relays are operated by the drop-bail instrument whenever the regenerator'temperatures' deviate to agreater extent from the normal figure, these relays 'thus effecting a greater change in the fresh gas volumes. The mean value determination in Instead of the electrical transmission of the temperature measurement impulses and the electrical mean value determination as described above, it is possible to utilize similarly operating mechanical regulation apparatus. Jet tubes, for

example, may be used instead of the relays. 3| to 34, 4| to 44 and 5| to 54 and the contacts llll to I04, I to H4 and III to I24, and the contact rails 8| ,to84, d 9| to 94 may then be replaced by suitable ope rigs in the' switching apparatus.

Each individual control operationchanges the volume of the air, so that the temperature difference between separation product and air at the cold end of the regenerator in the permanent state is changed a certain amount, for example 2. The establishment of the new permanent state following each regulation takes several reversal periods also at the lower end of the regenerator. It, therefore, a regulation at the end of each regenerator period was attempted, an excess of control or regulation would result. Thisdifdculty may be obviated either by effecting a control operation only at intervals of from five to ten reversals, or by providing a suitable feed-back. The feed-back may preferably be accomplished by electrical means, in that simultaneously with the regulating operation, the bridge formed by two thermometers H and I2 or l3 and I4 is so adjusted by the insertion or shunting of additional resistances, that the change in the temperature diiference in the state of equilibrium corresponding to one operation had already partly taken place, for example, to one-third. The feedback is or may be cancelled at the subsequent' A satisfactory supervision of the operations and the control of the operations may be combined in a simple manner with the distribution of the fresh gas volumes to the individual regenerators. For this purpose, for .example, red signal lamps may be simultaneously operated with the relays 3| to 34, white lamps with the relays 4| to 44,

and green lamps with the relays to 54. These lamps would immediately inform the supervising personnel whether or not a particular regenerator is at the normal temperature. Likewise, the impulses of the relays 3| to 34, 4| to 44 or 5| to 54 can be transmitted ,to a multiple-recorder, whereby either the temperatures of the regenerators or the individual. regulations following the mean value determinations may be recorded, as desired for purposes of supervision and control.

The above-described methods of and means for automatically regulating, supervising, or controlling gas volumes flowing through regenerators by means of measuring the temperatures and regulating the deviations from the mean value, may be applied also to any case in which a volume, temperature or concentration is to be controlled on the basis of a measurement of a variable, by several apparatus of the same kind which are connected in parallel or in series, whereby the total volume, the total temperature or the total concentration is to be governed from a predetermined initial value, or is to result in a certain final value. We may mention, by way of example, the case in which a plurality of air compressors of different capacity are operated in parallel and it is desired to obtain a given total or final pressure with a minimum power consumption, or when all stages of a multi-stage compressor are to bear an equal load. 4

A further example of a possible method of regulation in accordance with the present invention 1. Method of distributing gaseous fluids supplied in constant total quantity to a plurality of heat exchange devices which includes varying automatically the amount of gas entering each' of said devices in accordance-With the variations in temperature between the temperature of the gas discharged by said devices and an assumed normal discharge temperature.

' 2 In the separation of gas mixtures into their components by removing heat therefrom, the method of distributing said gases to a plurality of heat exchange devices, and varying the volumes of gas entering each of said devices in inverse proportion to. the temperature increment of the gas discharged from said devices above a predetermined reference'temperature.

3. Method as defined in claim 2; which comprises controlling the gas volumes by means electrically responsive to said temperature variations.

4. Method for automatically controlling the distribution of a gaseous fluid which is to cooled, which comprises conducting said fluid through a plurality of heat exchange devices or regenerators, individually measuring the temper-- ature of the fiuid at eachof s'aid devices, deter-' mining the mean value of said individual temperature measurements, and effecting a change in the gas supply to only those regenerators whose temperature deviates from this mean value..

5. Method as defined in claim 4, which comiprises determining the mean value of the inditemperature control measurement from a predetermined normal figure.

6. The method of controlling the distribution of gas through heat exchange devices, which comprises determining the temperature of the gas flowing through each of said devices, computing the average temperature for the gases flowing through all of the said devices, and acting upon the gas flow of those of said devices whose gas temperature deviates from said average temperature.

7. System for automatically controlling the distribution of a gaseous fluid to a plurality of heat exchange device's, comprising means for transmitting impulses according to the temperature variations of said devices, means for determining the mean value of said variations in temperature and for storing the net effect of said impulses responsive to said variations, said means including' a rotary switching disk provided with two sets of partly circular rails which are adapted to be displaced by the deviations of the individual regulating measurements from a predetermined normal value, a plurality of relays, and means for connecting said contacts to those relays only which were operated by a control measurement which deviated from the said mean value.-

8. System according to claim 7, characterized inthat for each heat exchange device there is provided a group of relays and two contact rails conductively connected to control relays, so that when the switching disk is in its neutral position all of the contact rails terminate symmetrically with respect to the relays which are operative at the normal temperature, whereas the distance from one rail set to the other corresponds to as many individual displacements of the disk as there are heat exchange devices.

9. System according to claim 7, characterized by the provision of circuit preparing relays and indicating devices whichare operated simultaneously with the rotation of said disc.

tions or regulations of the temperatures measured by said thermometers.

11. In the separation of gas mixtures into their components by removing heat therefrom, the

method comprising, supplying a constant quantity of the gas to be separated, distributing said gases among a plurality of heat-exchange devices arranged in pairs, by controlling the proportionate amount of the gas entering each of said devices in accordance with the difierence'in temperature existing between the two' devices of one pair.

12. In the separation of gas mixtures into products of separation by removing heat therefrom, the method comprisingsupplying a substantially constant quantity of the gas to be separated, cooling a plurality of heat-exchange devices with the products of separation, and controlling the ucts of separation by means of cold accumulators arranged in pairs, the steps comprising, maintaining the periods between reversals of flow through said accumulators substantially constant, and apportioning the quantity of gas mixture between the accumulators of each pair in accordance with the temperature of the mixture leaving the accumulators.

14. In a method of separating a gas mixture into its components at low temperature wherein the mixture is cooled by heat exchange with products of separation by means of cold accumulators arranged in pairs, the steps comprising, maintaining the periods between reversals of flow through said accumulators substantially constant, and reducing the proportion of gas mixture passing through one accumulator of a pair in response to a rise in temperature of the gas mixture leaving said accumulator.

'15. In a method of separating a gas mixture into its components at low temperature wherein the mixture is cooled by heat exchange with products of separation by means of cold accumulators arranged in pairs, the steps comprising, maintaining the periods between reversals of flow through said accumulators substantially constant, supplying the .gas mixture in substantially constant total quantity, and changing the quantity of gas mixture supplied to any one of said accumulators iii-response to a variation in tem- 0 perature of the cold portion thereof from the mean temperature value of the cold portions of all the accumulators.

16. In a method of separating a gas mixture into its components at low temperature wherein the mixture is cooled by heat exchange with'products of separation by means of cold accumulators arranged in pairs, the steps comprising, maintaining the periods between reversals of flow 5 through said accumulators substantially constant, supplying the gas mixture in substantially constant total quantity, controlling the amount of gas mixture admitted to each of said accumulators in response to variations in the difference 10 in temperature between the mixture and the products of separation at the cold end of the accumulator, and regulating the distribution of the mixture among the accumulators in accordance with variations of the temperature of the cold 15 ends thereof from a. desired temperature level.

17. System for automatically controlling the distribution of a gas mixture to be cooled 5 a plurality of accumulators arranged in pairs comprising, ineans for automatically reversing the -20 flow through said accumulators at constant time intervals, means for individually regulating the quantity of gas mixture supplied to each accumulator, means for producing intermittent impulses when the temperature of the fluid discharged from any one of said accumulators varies from a desired value, and means for causing said impulses to actuate said individual regulating means to change the quantity of gas mixture supplied to said accumulator so as to counteract said variation.

PHILIPP BORCHARDT. HANS RANKE. 

